Biomechanical Characterization of Subclinical Keratoconus Without Topographic or Tomographic Abnormalities

PURPOSE: To present a case series of patients with subclinical keratoconus with normal topometric (anterior curvature) and tomographic findings in one eye who showed abnormalities detected by Corvis ST (Oculus Optikgerate GmbH, Wetzlar, Germany) in vivo biomechanical assessment. METHODS: All patients had a complete ophthalmic examination, including the Corvis ST biomechanical measurements, optical tomography, and pachymetry with Pentacam (Oculus Optikgerate GmbH), and Placido-based topography with either the Nidek (OPD III Nidek, Gamagori, Japan) or CSO platform (Costruzione Strumenti Oftalmici, Florence, Italy). Inclusion criteria were a clinical diagnosis of ectasia in one eye and normal topometric and tomographic findings in the fellow eye (subclinical keratoconus), including a Belin/Ambrosio Enhanced Ectasia total deviation index from the Pentacam with less than 1.6 standard deviations from normative values and a Corvis Biomechanical Index score of greater than 0.5 in both eyes. RESULTS: Tomographic and topographic analysis was normal in one eye and abnormal in the fellow eye in 12 patients. The biomechanical results with the Corvis Biomechanical Index were shown to be abnormal in both eyes of all patients and aided the diagnosis. CONCLUSIONS: Biomechanical analysis showed abnormalities, whereas tomography and topography were normal. Basing on these findings, the authors suggest the use of biomechanics as an additional diagnostic tool.